PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Photosynthetic capacity of young and old leaves of sweetgum trees grown in elevated atmospheric CO2.
Thomas, Richard1, van Bloem, Skip1, Briden, Sarah1, Herrick, Jeffrey2, 1 West Virginia University, Morgantown, WV, US2 Environmental Protection Agency, Research Triangle Park, NC, US
ABSTRACT- The Duke Forest Free Atmospheric CO2 Enrichment (FACE) experiment consists of a loblolly pine forest with three control plots and three plots that have been fumigated with elevated CO2 (ambient plus 200 ppm) since August 1996. Since that time we have been monitoring the effects of CO2 enrichment on photosynthetic capacity of overstory sweetgum (Liquidambar styraciflua ) trees that were naturally established in the forest. Previously (1997-1999), we found a strong enhancement of photosynthesis and no down-regulation of photosynthesis of the sweetgum trees by elevated CO2. In this study, we used three years of measurements to examine whether there was a differential effect of CO2 on photosynthetic capacity of young and old sweetgum leaves. During early September of 2000, 2001 and 2004, we measured Asat (light-saturated net photosynthetic rate) versus Ci (calculated intercellular CO2) on fully developed sun leaves that had broken bud in early spring (old) and sun leaves that initiated in mid-June (young). Averaged across all years, elevated CO2 stimulated light-saturated net photosynthesis by 42% in leaves of both age. Asat of older leaves was reduced by 26% compared to the younger leaves. This was reflected by similar reductions in the maximum rate of carboxylation (Vcmax, from A-Ci curves) and electron transport (Jmax) in the older leaves. Vcmax and Jmax was not affected by CO2 enrichment during any year of this study. Thus, we found no evidence of a differential photosynthetic response to elevated CO2 in old and young sweetgum leaves and, despite a decline in photosynthetic capacity with age, old sun leaves also did not acclimate to CO2 enrichment.
Key words: elevated co2, forest trees, photosynthesis, nitrogen